WO2006092527A1

WO2006092527A1 - Method for optimized transient-phase regulation in a turbocharger

Info

Publication number: WO2006092527A1
Application number: PCT/FR2006/050172
Authority: WO
Inventors: Laurent Fontvieille
Original assignee: Renault S.A.S
Priority date: 2005-02-28
Filing date: 2006-02-27
Publication date: 2006-09-08
Also published as: EP1856390A1; FR2882576A1; FR2882576B1

Abstract

The invention concerns a method for controlling an engine (10), characterized in that it includes a step of regulating a quantity related to a turbocharger (60) around a setpoint (111), and in that it consists in determining a maximum value for the setpoint, based on a parameter characterizing the operation of the turbocharger, such that during a transient phase the regulated quantity related to the turbocharger is kept lower than the maximum value.

Description

DASN TRANSIENT PHASE OPTIMIZED REGULATION PROCESS A TURBOCOMPRESSOR

The present invention relates to the field of control of an engine.

More particularly, the invention relates to a method of controlling a vehicle engine and a system for adjusting a boost pressure in an intake manifold of an engine.

The use of such a method and such a system is particularly advantageous in diesel engines supercharged by a turbocharger.

Motor vehicles, and in particular diesel-type motor vehicles, are very often equipped with an air turbocharger of the engine in air, intended to increase the amount of air admitted into the cylinders.

This turbocharger generally comprises a turbine, placed at the outlet of the exhaust manifold of the engine and driven by the exhaust gas.

It further comprises a compressor, for example mounted on the same axis as the turbine, providing a compression of the air entering the intake manifold.

In this case, the turbocharger is associated with an exhaust gas control member for regulating the pressure in the intake manifold around a pressure setpoint developed, for example, by prior learning , depending on engine speed and fuel flow.

Such an adjusting member may be a discharge valve, or fins, in the case of a variable geometry turbocharger.

Alternatively, an exchanger may be placed between the compressor and the intake manifold to cool the air at the outlet of the compressor.

Moreover, we are nowadays equipped with standard type engines a diesel particulate filter, mounted on the engine exhaust line, to minimize the amount of particulate matter released to the atmosphere

(black smoke)

These filters typically include a set of microchannels in which a large part of the particles is trapped.

Once the filter is full, it is necessary to implement a regeneration phase, consisting essentially of emptying the filter by burning the particles.

This regeneration can be obtained either by a heating device provided for this purpose, or by providing phases of operation of the engine according to specific parameters.

The particulate filter being placed in the exhaust line after the turbocharger, the introduction of such a device generates a rise in pressure at the outlet of the turbine of the turbocharger. This increase in pressure, which is all the more important that the filter is loaded with particles, results in a reduction of the expansion rate in the turbocharger, thus by a reduction of the power provided by the exhaust gas to the turbine and by a consequent decrease in engine performance. In order to maintain the same level of performance, it is necessary to keep the expansion ratio substantially constant, which generally leads to the desire to increase the inlet pressure of the turbine.

Such a pressure increase is generally obtained by acting on said adjustment member. For example, in the case where the turbocharger is associated with a relief valve, it suffices to act on the closure of this valve or in the case where the turbine has fins to adjust the power of the exhaust gas it is sufficient to modulate the degree of opening thereof.

Moreover, such an operation is typically controlled by a central unit which will regulate for example the supercharging pressure in the manifold as a function of the pressure measured in the intake manifold and a setpoint.

In this regard, reference may be made in particular to document US 2003/0010019 where it is added a regulation of the inlet pressure of the turbine to a regulation of the supercharging pressure in the manifold. In order to obtain a response time as short as possible from such a control loop, it is also possible to add one or more pre-positioning value (s) so as to converge it more rapidly towards a desired value, the latter allowing for example to obtain a desired power of the exhaust gas by adequate modulation of the blades of the turbine.

This pre-positioning value may for example be in the form of a map based on the engine speed and a fuel flow.

By reading this map, it is thus possible to obtain an optimum pre-positioning value for a given operating state of the engine, namely in this example for a given engine speed and fuel flow.

Although having rendered many services, such systems nevertheless pose problems, especially when these types of regulation are in a transient phase, that is to say in a non-stationary phase. For example, in the case of the above-mentioned system, when the variation of the engine speed or the fuel flow is greater than a certain threshold, the regulation of the expansion ratio may temporarily be mismatched and in particular lead to operate the turbocharger in a zone non-optimal operation.

In particular, it is possible that the regulation forces the turbocharger to operate in an operating zone where its efficiency is low, which more generally penalizes the engine performance. An object of the invention is therefore to provide a method for improving the performance of this type of engine when it is in a transient operating state.

For this purpose, a method of controlling an engine is proposed according to the invention, characterized in that it comprises a step of regulating a quantity relative to a turbocharger around a setpoint, and in that the a maximum value is determined for the setpoint, which depends on a parameter characterizing the operation of the turbocharger, so that during a transient phase the regulated variable relative to the turbocharger remains below the maximum value. Preferred but non-limiting aspects of the process according to the invention are the following:

- The setpoint is a PiT∞ns set point of expansion of the turbocharger;

- the parameter that characterizes the operation of the turbocharger turbocharger power;

the maximum value PiThm of the set point PiTcons is determined relaxing from the equation:

where Qt is a flow of exhaust gas passing through the turbine, Wt the power of the turbocharger, Cpe _* a constant corresponding to a specific heat of the exhaust gas, T3 a temperature upstream of the turbine, ηt, mm a setpoint of minimum efficiency of the turbine and γ _e χ a constant corresponding to a specific heat ratio for the exhaust gas;

the power Wt of the turbocharger is determined by the power Wc of the compressor which constitutes it in part;

the power Wc of the compressor is determined from the equation:

W _c = Q _c .C _Pai , Tl. - 1 + T] ₀ - 1

where Qc represents a flow of air passing through the compressor, Cpa.r is a constant corresponding to the specific heat of the air, Tl a temperature measured at the input of the compressor, η _c a compressor efficiency, P2 and P1 of the measured pressures respectively at the input and at the output of the compressor and γr a note corresponding to a specific heat ratio for the air;

the power of the turbocharger is determined by the power Wt at the turbine, in particular by the equation:

where NT is a turbocharger regime, N is a time derivative of the turbocharger regime, IT is a constant corresponding to an inertia of the turbocharger and DT a constant corresponding to a turbocharger friction;

the method further comprises a step of regulating a supercharging pressure in an intake manifold of the engine; - A result of the regulation of the relative size of the turbocharger is a function of a result of the regulation of the boost pressure.

The invention also proposes a control system for an engine, comprising at least one turbocharger and a regulator for regulating a quantity relative to this turbocharger around a setpoint, characterized in that it furthermore comprises means capable of determining a maximum value for the setpoint, said value depending on a parameter characterizing the operation of the turbocharger, so that during a transient phase the regulated variable relative to the turbocharger remains below the maximum value. Preferred but non-limiting aspects of the system according to the invention are the following:

the magnitude is a rate of expansion of the turbocharger;

- The setpoint is a PiT∞ns set point of expansion of the turbocharger; the system comprises a second regulator for regulating a boost pressure in an engine intake manifold;

- A regulator input of the relative size of the turbocharger is a function of an output of the regulator of the boost pressure.

Thus, the control method according to the invention offers many advantages over the methods and systems of the prior art.

In particular, during a transient phase of a regulation according to the invention, one takes into account on the one hand a particular demand of a driver (acceleration, etc.) and on the other hand the actual operating conditions of the turbocharger. By way of non-limiting example, when a variation of the fuel flow is required under the request of the driver, the method of the invention uses data corresponding to the state of operation of the turbocharger in real time to allow that during this transitional phase the regulation remains optimal. Optimum regulation means that the regulation is always adapted.

By way of nonlimiting example, a suitable regulation is a regulation such that the turbocharger operates constantly in a zone of high efficiency, thus leading to a maintenance of good engine performance, in particular during the transient regime.

Other aspects, objects and advantages of the invention will appear better on reading the following description of the invention, with reference to the appended drawings in which:

FIG. 1 represents a motor unit according to the invention; FIG. 2 represents a more detailed embodiment of the motor unit of FIG. 1; FIG. 3 schematically shows, by way of example, an implementation of a regulation structure according to the invention used in the embodiment of FIG. 2,

FIG. 4 shows a representative block diagram of the calculation of a compressor efficiency,

FIG. 5 shows a representative block diagram of the calculation of a turbocharger speed,

FIG. 6 shows a representative block diagram of the calculation of a limitation of an expansion ratio in the turbocharger turbine; FIG. 7 shows a time simulation of the operation of a system of the invention.

Referring now to FIG. 1, there is shown a motor unit 1 of the invention comprising an internal combustion engine 10 of a motor vehicle, of diesel type, supplied with fresh air by an inlet 20 and which rejects the gases burned by exhaust 30.

The fresh air intake circuit in the engine 10 essentially comprises an air filter 40 and an air flow meter 50 supplying, via a turbocharger 60 and appropriate conduits, the intake manifold 70 of the engine 10. An exhaust manifold 80 recovers the exhaust gases from the combustion and discharges the latter outwards, via the turbocharger 60 and a particulate filter 90 for reducing the amount of particles , including soot, released into the environment.

As regards the turbocharger 60, it essentially comprises a turbine 61 driven by the exhaust gas and a compressor 62 mounted on the same axis as the turbine 61 and providing a compression of the air distributed by the air filter 40, in order to increase the amount of air admitted into the engine cylinders via an EGR circuit of exhaust gas recirculation.

A central unit 110 recovers, by means of appropriate sensors, pressure measurement signals Pm or pressure difference ΔP _m .

These measurements, as well as corresponding setpoints 111 determined within the central unit, are provided at the input of a regulation structure 113 included in said central unit 110. As will be seen, the regulation structure 113 may comprise one or more regulators.

And in the latter case, the regulators may be arranged in a cascade configuration or any other configuration known to those skilled in the art.

The regulation structure 113 also takes into account data provided by a block 112.

The data of this block makes it possible to limit at least one setpoint 111 to a maximum value so as to limit the regulation during a transient phase and thus obtain better motor performance as previously proposed. For this purpose, it is also expected that the control structure 113 provides a control signal 120 which controls a member associated with the turbine of the turbocharger to change in particular the power of the exhaust gas.

Furthermore, according to the invention, said maximum value for which the setpoint is limited is determined from at least one variable characterizing a turbocharger operation. In particular, in a preferred embodiment of the invention this magnitude is the rate of expansion in the turbine.

In this way, during a transient phase, the limitation of the regulation 113 makes it possible to maintain optimum operation and performance of the turbocharger.

Figure 2 now shows a non-limiting and more detailed embodiment of the invention.

The elements of Figure 1 are generally found.

However, it can be seen that the central unit 110 receives as input a boost pressure P2m in the intake manifold 70, a pressure P3m at the inlet of the turbine 61 and a pressure P4m at the output thereof.

As mentioned above, the unit 110 can also receive a differential pressure, such as that present at the terminals of an EGR circuit, that is to say between the intake manifold 70 and the inlet of the turbine 61 .

These pressure measurements and the corresponding instructions are provided at the input of a cascade control structure that includes the central unit 110.

As mentioned previously, such a structure may comprise several regulators.

By way of example, FIG. 2 shows two regulators 113 ', 113 "in series.

The first regulator 113 'makes it possible to regulate a supercharging pressure in the intake manifold 70 and the second regulator 113' makes it possible to regulate an expansion ratio of the turbine 61. In this respect, the central unit receives as input the measurements P2m, P4m and P3m respective supercharging pressures, turbine output and in the exhaust manifold so as to determine the expansion rate PiTm in the turbine according to one of the following equations:

P2 _m + P3 / 2 _m _OR h _/ PPiiTT _mm == - _p4 - (2)

where P3 / 2m is the differential pressure across the EGR circuit.

The value PiTm obtained is then supplied to the input of the second regulator 113 ", namely the regulator of the expansion ratio in the turbine (see FIG. 3).

As shown again in Figure 2, the block 112 is interposed between the first and second regulators.

In this embodiment of the invention, this block 112 makes it possible to limit the regulation of the expansion ratio during a transient phase by limiting the setpoint PiT∞ns to the maximum value.

For this purpose, there is shown in Figure 3 a more detailed view of the regulatory structure adopted in this preferred embodiment of the invention. The regulator 113 'receives as input the difference between the setpoint P2c _0ns and the measurement P2m of the boost pressure.

It will be noted here that the setpoint P2coπs of the boost pressure is mapped in engine speed and fuel flow.

The output of the regulator 113 'is then added to an initial setpoint PiT∞πsj associated with the expansion ratio of the turbine, this first setpoint being also mapped in engine speed and fuel flow and representing the value around which the rate of expansion would be regulated if the limitation by the process did not take place.

The result of this sum is then compared by the block 115 to a maximum allowed value PiThm of the flash rate reference.

This maximum value PiThm is determined in real time by the central unit according to a calculation mode that will be described below.

The block 115 outputs a final set point PiT∞ns relaxation rate, the latter corresponding to a minimum between the value of said result and said maximum allowable value PiThm rate of expansion in the turbine.

Thus, as will be understood, the output of the block 115 is always lower than the maximum allowed value PiThm of the relaxation ratio setpoint.

The second regulator 113 "then receives at its inputs the difference between the output of the block 115 and a measurement PiTm of the expansion ratio in the turbine so as to develop the control signal 120 for controlling the member associated with the turbine, typically the fins.

It will be noted in passing that this control signal 120 also depends on a pre-positioning. Thus, in the example represented here in a nonlimiting manner, the output of the second regulator 113 "is added to a pre-positioning value obtained from a pre-positioning map 200, for example a map based on the engine speed and fuel flow.

We will now describe a calculation mode of the maximum allowable value PiThm of expansion ratio in the turbine.

According to the invention, this value is determined from at least one magnitude characterizing a turbocharger operation.

In particular, it has been seen that in the preferred embodiment of the invention this magnitude is the rate of expansion in the turbine.

However, it is recalled that other quantities are possible, such as the differential pressure at the terminals of the turbine; the key is that this magnitude can provide information on selected conditions of operation of the turbocharger.

In order to determine said maximum allowed value PiTi.m, the central unit calculates the following equation:

γ κτ _lim = (iw; V ^γ '^" (3)

where Qt is a flow of exhaust gas passing through the turbine, Wt the power of the turbocharger, Cp _ex a constant corresponding to a specific heat of the exhaust gas, T3 a temperature upstream of the turbine, ηt.mm a setpoint of minimum efficiency of the turbine and γ _ex a constant corresponding to a specific heat ratio for the exhaust gas.

Thus, as can be seen in this example, the maximum value of the quantity, and therefore of the expansion ratio, is determined using a power of the turbocharger.

According to one aspect of the invention, the power of the turbocharger is approximated by a power Wc of the compressor which constitutes it in part, in which case Wt in equation (3) is equal to Wc. However, according to a preferred aspect of the application, the power of the Turbocharger is determined from the respective powers of the compressor and the turbine.

For this purpose, the central unit first determines the power Wc of the compressor and then the power Wt to the turbine.

The compressor power is obtained from the following equation:

W _c

where Qc represents a flow of air passing through the compressor, Cpa.r is a constant corresponding to the specific heat of the air, Tl a temperature measured at the input of the compressor, η _c a compressor efficiency, P2 and P1 of the measured pressures respectively at the input and at the output of the compressor and γ _r a note corresponding to a specific heat ratio for the air.

As we can see, the computation of the power Wc of the compressor depends on four variables, in particular the variables Qc, Pl, P2 and Tl.

Furthermore the air flow Qc through the compressor can be advantageously equal to a fresh air flow, noted Qa.r.fra.s.

In this way, such a flow rate can be measured by a hot wire sensor placed at the outlet of the air filter.

It will further be noted that the power Wc of the compressor depends on the efficiency η _c of the turbocharger. This yield can be measured or estimated using a map function of engine operating conditions.

In this example, the mapping admits as input variable on the one hand the air flow rate Qc passing through the compressor corrected in temperature by the variable Tl as well as in pressure by the variable P1 and on the other hand by a ratio compression P2 / P1, which can be otherwise described by:

where f _n designates a function. We can also refer to Figure 4 schematically showing the calculation of the variable η _c using the mapping and input variables of the latter.

As far as the turbine power calculation is concerned, the CPU uses the following equation:

W _t = N _τ . Nτ .I _τ + N _τ .D _τ + W _C (6)

where NT is a turbocharger regime, N is a time derivative of the turbocharger regime, IT is a constant corresponding to an inertia of the turbocharger and DT a constant corresponding to a turbocharger friction.

This calculation therefore uses three input variables, namely the power Wc

of the compressor, the turbocharger NT speed and the NT derivative of the turbocharger regime.

The NT variable corresponding to the turbocharger speed can be measured or estimated.

In the latter case, it is estimated from a compressor field which is mapped to a compressor flow rate Qc corrected in temperature and pressure and in compression ratio P2 / P1 (see FIG. 5 where the symbol * designates a multiplication operation) .

Therefore the turbocharger NT regime can be defined by the following expression:

where fN, Tref and Pref respectively denote a function, a reference temperature and a reference pressure. Figure 6 gives a schematic representation of the estimation calculation of the NT turbocharger regime.

Once the power Wt at the turbine determined, the central unit is able to determine the maximum allowable value PiTi _™ relaxation rate in the turbocharger by injecting WT in equation (3). To return to the calculation of PiTi.m, it will be noted that the flow rate Qt of gas passing through the turbine can be evaluated by adding the flow of fresh air measured.

Qair.fra.s through the flowmeter at a Qcarb fuel flow.

In addition, the inlet temperature T3 of the turbine can be measured or estimated. Such an estimate can be obtained from a map depending on engine speed and fuel flow.

Preferably, the central unit causes the estimate obtained from this map to be delayed by 1.5 engine revolutions in order to take into account the four-stroke cycle of the engine, and then filtered in the first order to simulate a thermal inertia. exhaust manifold.

Of course, those skilled in the art will obviously adapt the retardation value and the type of filtering in the case of engines of different types.

As regards now the variable ηt.mm in equation (3), it is important to note that this is a threshold for setting the limiting level of the regulation of the boost pressure and in particular the level of limitation of the expansion ratio in the turbine.

According to the invention, this variable is either a constant or estimated from a mapping function of the turbocharger speed and the position and the operating state of said member associated with the turbocharger.

By way of non-limiting example, in the case where the member concerns blades of the turbine, it may be their position.

Reference can be made in this regard to FIG. 6 schematically showing this example of calculating the variable ηt, mm as a function of the measured position VNT _pos of the fins.

Of course, those skilled in the art will understand that this variable VNTpo can also be estimated from the knowledge of operating parameter of the engine. Figure 7 now shows a time simulation of the engine block as described above to analyze its operation when it is in particular in a transitional phase.

Figure 7A shows two pressure curves as a function of time.

The first curve 201 is a simulation of the measured supercharging pressure P2 _m and the curve 202 that the measured pressure P3m in the exhaust manifold (or in other words at the inlet of the turbine).

As can be seen, the motor enters the transient phase at time t = 15s and comes out at about t = 20s.

FIG. 7B shows a simulation 203 corresponding to the estimate NT of the engine speed and in FIG. 7C that of the calculation of the power of the compressor and the turbine, respectively 204 and 205.

Finally, Figure 7D clearly illustrates the process of the invention.

Indeed, it can be seen that during the transient phase (t between about 15s and 20s) the curve 206 corresponding to the simulation of the measurement of the expansion factor PiTm is glued to the curve 207 representing the estimate of the maximum authorized value PiThm relaxation rate.

The limitation of the regulation of the boost pressure is therefore active and moreover optimized in real time for the operating conditions of the turbocharger.

In particular, thanks to the method of the invention, the regulation is such that the expansion ratio is never equal to a value that would limit the performance of the turbocharger, especially in a low efficiency operating range due to a rate of expansion too high.

Returning to FIG. 7D, it can furthermore be seen that once the transient phase has been completed, the limitation of the trigger ratio set point, or indirectly that of the booster pressure regulation P2 _™ , is no longer active ( from approximately t = 20s). Indeed, in the stationary state after t = 20s, the curve 206 reaches much higher levels than the curve 207; these two curves do not evolve together anymore.

Naturally, the invention is not limited to the form described above and the skilled person can adapt it in many ways without departing from its fundamental principle.

In particular, it is obvious that an estimate of a variable can be made from another means than mapping.

The use of an estimation algorithm, such as a Kalman filter or other, can in particular be considered.

Claims

1. A method of controlling an engine (10), characterized in that it comprises a step of regulating a magnitude relative to a turbocharger (60) around a setpoint (111), and in that the a maximum value is determined for the setpoint, which depends on a parameter characterizing the operation of the turbocharger, so that during a transient phase the regulated variable relative to the turbocharger remains below the maximum value.

2. Control method according to claim 1, characterized in that the magnitude is an expansion ratio of the turbocharger (60).

3. Control method according to one of the preceding claims, characterized in that the setpoint (111) is a set PiT∞ns relaxation rate of the turbocharger (60).

4. Control method according to one of the preceding claims, characterized in that the parameter which characterizes the operation of the turbocharger (60) power of the turbocharger (60).

5. Control method according to the preceding claim, characterized in that the maximum value PiTum of the set point PiT∞πs of the expansion ratio is determined from the equation:

where Qt is a flow of exhaust gas passing through the turbine (61), Wt the power of the turbocharger (60), Cp _C χ a constant corresponding to a specific heat of the exhaust gas, T3 a temperature upstream of the turbine , ηt, min a turbine minimum efficiency reference (61) and γ _™ a constant corresponding to a specific heat ratio for the exhaust gas.

6. Control method according to the preceding claim, characterized in that the power Wt of the turbocharger (60) is determined by the power

Wc of the compressor (62) which constitutes it in part.

7. Control method according to claim 6, characterized in that the power Wc of the compressor (62) is determined from the equation:

1

where Qc represents a flow of air passing through the compressor, Cpmr is a constant corresponding to the specific heat of the air, Tl a temperature measured at the input of the compressor (62), η _c a compressor efficiency (62), P2 and Pl measured pressures respectively input and output of the compressor (62) and γ _r a report corresponding to a specific heat ratio for air.

8. Control method according to claim 6, characterized in that the turbocharger power (60) is determined by the power Wt at the turbine (6I) _{7 in} particular by the equation:

where NT is a turbocharger regime (60), N is a time derivative of turbocharger speed (60), IT is a constant corresponding to an inertia of the turbocharger (60) and DT a constant corresponding to a turbocharger friction (60).

9. Control method according to one of the preceding claims, characterized in that it further comprises a step of regulating a supercharging pressure in an intake manifold (70) of the engine (10).

10. A control method according to claim 9, characterized in that a result of the regulation of the magnitude relative to the turbocharger (60) is a function of a result of the regulation of the supercharging pressure.

11. A control system of an engine (10), comprising at least one turbocharger (60) and a regulator (113 ") for regulating a quantity relative to this turbocharger around a set point (111), characterized in that it further comprises means capable of determining a maximum value for the setpoint, said value depending on a parameter characterizing the operation of the turbocharger (60), so that during a phase transient the regulated variable relative to the turbocharger remains lower than the maximum value.

12. System according to claim 11, characterized in that the magnitude is an expansion ratio of the turbocharger (60).

13. System according to one of claims 11 to 12, characterized in that the setpoint is a PiTcons set point of expansion of the turbocharger (60).

14. System according to one of claims 11 to 13, characterized in that it comprises a second regulator (113 ') for regulating a supercharging pressure in an intake manifold (70) of the engine (10).

15. System according to claim 14, characterized in that an input of the regulator (113 ") of the magnitude relative to the turbocharger is a function of an output of the regulator (113 ') of the supercharging pressure.